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Structural Geology

Structural Geology. Faulting. Structural Geology. Folding. Terminology. Stress – The force acting on a surface, force per unit area Deformation – change in shape or volume of rock in response to stress Strain – deformation resulting from stress. Stress. Uniform – compressional

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Structural Geology

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  1. Structural Geology Faulting

  2. Structural Geology Folding

  3. Terminology • Stress – The force acting on a surface, force per unit area • Deformation – change in shape or volume of rock in response to stress • Strain – deformation resulting from stress.

  4. Stress Uniform – compressional Differential – compressional tensional shear

  5. Types of Stress • Uniform stress – equal force applied in each direction

  6. Types of Stress • Differential stress – force applied is greater in one direction

  7. Types of Differential Stress

  8. Deformation (strain) 1. Elastic – nonpermanent, rock returns to original shape 2. Ductile (plastic) – permanent, rock flows or bends 3. Brittle – permanent, rock breaks

  9. Faults (brittle strain) All of the faults occur in this region as the Earth is broken. Brittle Deformation Region Normal, Reverse, and Strike-slip faults Fracture point Folds (ductile strain) All of the folds occur in this region as the Earth is bent but not broken. Ductile Deformation Region Anticlines, Synclines, Monoclines, Basins, Domes Stress (a compressional, tensional, or shear force) Elastic Limit point Earthquakes (elastic strain) Earthquakes occur in this region due to Elastic Rebound There is NO permanent deformation This does not create a break in the Earth. The earth is already broken. This is just slippage along the break. Elastic Deformation Region

  10. Types of Deformation (Strain) • 1. Elastic deformation – material returns to its original shape after stress is removed. • Example: rubber band Elastic limit – point beyond which permanent deformation occurs.

  11. Types of Deformation (Strain) • 2. Ductile (plastic) deformation – permanent change in shape by bending or flowing. • Example: copper wire

  12. Types of Deformation (Strain) • 3. Brittle deformation – permanent change in shape when the material fractures or cracks • Example: breaking a piece of slate

  13. Factors affecting Deformation • Temperature – as temperature increases, materials become more ductile. • Example: plastic 2. Confining Pressure – as pressure increases (weight of overlying rocks), materials become more ductile.

  14. Factors affecting Deformation 3. Rate of deformation – if stress is applied rapidly, rocks will tend to be brittle. • Example: bit o-honey 4. Composition of rocks – at the same temperature and pressure, some rocks will be more brittle than others. Example: slate (brittle) and copper (ductile)

  15. Measuring Deformation in the RocksStrike & Dip

  16. Geologic Map

  17. Geologic Map Geologic Profile Geologic Cross Section

  18. Types of Faults • Classified by relative motion • Dip –Slip • Strike - Slip

  19. Dip – Slip • Normal • Reverse • High angle • Low angle

  20. Footwall and Hanging Wall

  21. Normal Fault

  22. Reverse Fault

  23. Strike – Slip

  24. http://earthquake.usgs.gov/regional/nca/virtualtour/bayarea.phphttp://earthquake.usgs.gov/regional/nca/virtualtour/bayarea.php

  25. Dip-Slip Faults Motion is up and down Normal Fault Reverse Fault Compressional Stress Tensional Stress Hanging Wall Block Foot Wall Block Hanging Wall Block Foot Wall Block Pushing Together Pulling Apart Convergent Boundary Divergent Boundary Strike-Slip Faults Motion is side-to-side Shear Stress Sliding Past Each Other Transform-Fault Boundary

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